Abstract
Low-quality tobacco leaves generally exhibit undesirable sensory characteristics due to excessive macromolecule accumulation and insufficient aroma release. Fermentation with functional microorganisms to improve tobacco quality is a green and efficient strategy. This study employed volatile flavoromics and microbiomics to investigate the flavor basis and underlying microbial regulatory mechanism for quality improvement by Bacillus subtilis DB-15. Results showed that B. subtilis DB-15 fermentation significantly degraded starch, protein, and cellulose, and comprehensively enhanced sensory quality by increasing aroma and sweetness while reducing irritation and off-flavors. Subsequently, a total of 94 volatile compounds were identified by HS-SPME-GC-MS. B. subtilis DB-15 promoted the enrichment of esters and heterocycles, and inhibited harmful substances such as short-chain fatty acids and nicotine. Microbiomics analysis indicated that inoculated B. subtilis DB-15 dominated the bacterial community and reshaped its structure, whereas fungal community succession was mainly driven by water addition rather than Bacillus inoculation. Functional prediction suggested a higher relative abundance of bacterial pathways related to carbohydrate and amino acid metabolism in the Bacillus inoculation group, whereas pathways related to terpenoid and polyketide metabolism showed lower predicted abundances. Correlation network analysis showed that Bacillus was positively correlated with sweet and fruity aroma compounds but negatively correlated with irritant acids, suggesting a potential contribution to improved sensory coordination. This study reveals the mechanism of sensory improvement by B. subtilis DB-15 fermentation from dual-omics perspective, providing a reliable technical strategy for upgrading low-quality tobacco resources.